Steps

Drag the Chartboost prefab in the Chartboost folder and the Admob prefab in the GoogleMobileAds into the first scene of your game

Fill out the fields on the AdmobController Script on the admob prefab, admob is now set up. For Chartboost click Chartboost -> Edit Settings at the top of Unity and fill out the Chartboost info, then click Setup Android SDK.